1. Field of the Invention
This invention relates to transport refrigeration systems. More particularly, this invention relates to a transport refrigeration system that automatically adjusts compressor discharge pressure using a suction modulation valve to reduce compressor cycling and increase pull-down capacity of the transport refrigeration unit.
2. Description of the Prior Art
Container refrigeration systems are known in the art for providing methods of limiting maximum head/condenser pressures. Conventional container refrigeration systems such as that employed in the THINLINE.RTM. series of transport refrigeration units manufactured by the Carrier Transicold Division of Carrier Corporation located in Syracuse, N.Y., typically include a condenser pressure control logic or the like to limit and maintain head/condenser pressures to a maximum value. Generally, these machines activate one or more condenser fans in response to an increasing ambient temperature to maintain discharge pressures below a predetermined maximum value in low temperatures. These conventional container refrigeration systems can employ air-cooled condensers and/or water-cooled condensers having some sort of water pressure switch such as a model 20SP117-7 manufactured by Texas Instruments to and/or a high pressure side transducer to help control the aforesaid high head/condenser pressures. It is well known by those skilled in the refrigeration art, that such systems are commonly susceptible to rapid compressor cycling during temperature pull-down periods in order to achieve the necessary refrigeration capacities. This rapid compressor cycling is disadvantageous in that it reduces compressor reliability and creates unwanted constant noise levels that become a nuisance to end users.
Still needed, but not available with transport refrigeration systems presently known in the art is a transport/container refrigeration system that is capable of establishing and maintaining maximum refrigeration system capacity during periods of temperature pull-down without necessitating rapid compressor cycling.